What is the function of len in python 3.6

Tell me please

The len() function in Python returns you the number of elements in case of a list and returns the number of characters in case of a string.

$>>> A = [1, 2, 'a', 4, 10000]
$>>> len(A) = 3 #Number of elements in the list  
$>>> string = 'Code Chef'  
$>>> len(string) = 9 #Number of characters including space

Also what does t-=1 means if t is a variable

t-=1 is the short notation for t = t - 1

len(A)=5 not 3.

@swetankmodi That’s technically not true. -= (__isub__) and - (__sub__) doesn’t have to be compatible with each other. I don’t know of a case in the standard libraries where it isn’t, but for the case of addition (+= and +) types like list behaves differently (+ combines into a new list, += is the same as extend). Similar things are true for | and & for set operations.